Auto adjusting balancer apparatus

ABSTRACT

An apparatus includes a string of serially-connected energy storage devices, a string of serially-connected windings on at least one core and having a first medial node coupled to a first medial node of the string of serially-connected energy storage devices, and first and second switches configured to connect first and second end nodes of the string of serially-connected storage devices to respective first and second end nodes of the string of serially-connected energy storage devices. A control circuit is configured to operate the first and second switches at the same duty cycle.

RELATED APPLICATION

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 15/467,475, entitled “POWER CONVERTER APPARATUS ANDMETHODS USING ADAPTIVE NODE BALANCING,” filed Mar. 23, 2017 andincorporated herein by reference in its entirety

BACKGROUND

The inventive subject matter relates to electrical apparatus and, moreparticularly, to power converter apparatus.

Power converter apparatus, such as uninterruptible power supply (UPS)systems, grid-tie inverters, and the like, commonly include an inverterthat receives power from a DC link. The inverter may produce a single orthree phase output that is referenced to a neutral, and the DC link mayinclude first and second buses that have respective positive andnegative voltages with respect to the neutral.

Unbalanced loads may cause DC bus imbalance problems in three phaseinverter systems. In particular, loading one phase of the inverteroutput more substantially than the other phases may result in animbalance in the voltages on the positive and negative DC buses of theDC link with respect to a neutral of the inverter. Such problems may beaddressed through the use of a “balancer” circuit that intermittentlycouples the DC buses to the neutral, as described, for example, in U.S.Pat. No. 6,483,730 to Johnson, Jr. et al. Such conventional balancercircuits may, however, generate undesirable ripple currents, even whenthe load is not unbalanced.

SUMMARY

Some embodiments of the inventive subject matter provide an apparatusincluding first, second, third and fourth serially connected windings, afirst switch configured to connect a first tap of the first winding to afirst terminal of a first energy storage device, and a second switchconfigured to connect a second tap of the first winding and a first tapof the second winding to a second terminal of the first energy storagedevice and first terminal of a second energy storage device. The secondtap of the second winding and a first tap of the third winding areconnected to a second terminal of the second energy storage device and afirst terminal of a third energy storage device. The apparatus furtherincludes a third switch configured to connect a second tap of the thirdwinding and a first tap of the fourth winding to a second terminal ofthe third energy storage device and a first terminal of a fourth energystorage device, and a fourth switch configured to connect a second tapof the fourth winding to a second terminal of the fourth energy storagedevice. A control circuit is configured to operate the first, second,third and fourth switches at a same duty cycle.

The first and second windings may be magnetically coupled to one anotherand the third and fourth windings may be magnetically coupled to oneanother. In some embodiments, the first and second windings may be woundon a first core and the third and fourth windings may be wound on asecond core. A turns ratio of the first winding to the second windingmay be 1:1 and wherein a turns ratio of the third winding to the fourthwinding may be 1:1.

In further embodiments, the first, second, third and fourth windings maybe magnetically coupled to one another. The first, second, third andfourth windings may be wound on a common core. A turns ratio of thefirst, second, third and fourth windings to one another may be 1:1.

In some embodiments, the duty cycle may be about 50%. In someembodiments, the duty cycle may be less than 40%.

In some embodiments, the apparatus may include a first diode connectedbetween the first terminal of the first energy storage device and thesecond terminal of the fourth winding and a second diode connectedbetween second terminal of the fourth energy storage device and firstterminal of the first winding.

The first, second, third and fourth energy storage devices may includecapacitors or batteries. The apparatus may include a multilevel invertercircuit coupled to the terminals of the first, second, third and fourthenergy storage devices.

Additional embodiments provide an apparatus including a string ofserially-connected energy storage devices, a string ofserially-connected windings on at least one core and having a firstmedial node coupled to a first medial node of the string ofserially-connected energy storage devices, and first and second switchesconfigured to connect first and second end nodes of the string ofserially-connected storage devices to respective first and second endnodes of the string of serially-connected energy storage devices. Acontrol circuit is configured to operate the first and second switchesat the same duty cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a bus balancer apparatusaccording to some embodiments.

FIG. 2 is a waveform diagram illustrating operations of the apparatus ofFIG. 1.

FIG. 3 is a schematic diagram illustrating a bus balancer apparatususing IGBT switching devices according to some embodiments.

FIG. 4 is a schematic diagram illustrating a bus balancer apparatusaccording to further embodiments.

FIG. 5 is a schematic diagram illustrating a bus balancer apparatus fora battery string according to some embodiments.

FIG. 6 is a schematic diagram illustrating use of a bus balancerapparatus with a 5-level inverter according to some embodiments.

FIG. 7 is a schematic diagram illustrating use of a bus balancerapparatus with a 7-level inverter according to some embodiments.

FIG. 8 is a schematic diagram illustrating an interleaved bus balancerapparatus according to some embodiments.

FIG. 9 is a waveform diagram illustrating operations of the apparatus ofFIG. 8.

DETAILED DESCRIPTION

Specific exemplary embodiments of the inventive subject matter now willbe described with reference to the accompanying drawings. This inventivesubject matter may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein;rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of the inventivesubject matter to those skilled in the art. In the drawings, likenumbers refer to like items. It will be understood that when an item isreferred to as being “connected” or “coupled” to another item, it can bedirectly connected or coupled to the other item or intervening items maybe present. As used herein the term “and/or” includes any and allcombinations of one or more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventivesubject matter. As used herein, the singular forms “a”, “an” and “the”are intended to include the plural forms as well, unless expresslystated otherwise. It will be further understood that the terms“includes,” “comprises,” “including” and/or “comprising,” when used inthis specification, specify the presence of stated features, integers,steps, operations, items, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, items, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this inventive subject matterbelongs. It will be further understood that terms, such as those definedin commonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of thespecification and the relevant art and will not be interpreted in anidealized or overly formal sense unless expressly so defined herein.

FIG. 1 illustrates a bus balancer apparatus 100 according to someembodiments of the inventive subject matter. The apparatus 100 isconfigured to balance voltages across four capacitors C1, C2, C3, C4that are serially connected between first and second DC buses 105 a, 105b. The apparatus 100 includes four series-connected windings L1, L2, L3,L4, here shown as wound in pairs on two cores 112 a, 112 b. A firstswitch S1 is configured to couple a first terminal of the first windingL1 to the first DC bus 105 a. A second switch S2 is configured toconnect a second terminal of the first winding L1 and a first terminalof the second winding L2 to a medial node of the string of capacitorsC1, C2, C3, C4 at which the first and second capacitors C1, C2 areconnected. A second terminal of the second winding L2 and a firstterminal of the third winding L3 are connected to a medial neutral nodeN at which the second and third capacitors C2, C3 are connected. In someembodiments, this node may not be tied to a neutral and the secondterminal of the second winding L2 and the first terminal of the thirdwinding could be coupled to this node via another switch (see, e.g.,FIG. 5). A third switch S3 is configured to connect a second terminal ofthe third winding L3 and a first terminal of the fourth winding L4 to amedial node of the string of capacitors C1, C2, C3, C4 at which thethird and fourth capacitors C3, C4 are connected. A fourth switch S4 isconfigured to connect a second terminal of the fourth winding L4 to thesecond DC bus 105 b. A first diode D1 is connected between the secondterminal of the fourth winding L4 and the first DC bus 105 a, and asecond diode D2 is connected between the first terminal of the firstwinding L1 and the second DC bus 105 b.

The windings L1, L2, L3, L4 preferably have an approximately 1:1 turnsratio, which is used to equalize voltages across the capacitors C1, C2,C3, C4. In some embodiments, a control circuit 120 controls the first,second, third and fourth switches S1, S2, S3, S4 such that the first,second, third and fourth switches S1, S2, S2, S3, S4 operate at thesubstantially the same duty cycle. More particularly, when the first,second, third and fourth switches S1, S2, S3, S4 are turned on, the 1:1turns ratio of the first, second, third and fourth windings L1, L2, L3,L4 drives the magnitudes of the voltages across the capacitors C1, C2,C3, C4 toward equilibrium. The first, second, third and fourth switchesS1, S2, S3, S4 are then turned off to initiate discharge of the first,second, third and fourth windings L1, L2, L3, L4 via the first andsecond diodes D1, D2 (which could be replaced by active switchingdevices that perform a similar function) and allow the flux in themagnetic cores 112 a, 112 b to fall to zero before the first, second,third and fourth switches S1, S2, S3, S4 are again turned on. In someembodiments, the first, second, third and fourth switches S1, S2, S3, S4may be operated at a duty cycle preferably slightly less than 50%, asshown in FIG. 2. In some embodiments, the duty cycle can be less thanshown in FIG. 2, although a significantly reduced duty cycle may lead toless desirable performance (e.g., increased ripple currents).

It will be understood that the apparatus 100 may be implemented usingany of a number of different types of components. In some embodiments,for example, the first, second, third and fourth S1, S2, S3, S4 may beimplemented using transistors, such as insulated gate bipolartransistors (IGBTs) or power MOSFETs, or other types of semiconductorswitches. Referring to FIG. 3, in an apparatus 100′, the first andfourth switches S1, S4 may be bidirectional switches formed using IGBTsQ1, Q6 with respective diodes D3, D8. MOSFETs can be similarly used, butcan have intrinsic body diodes that can eliminate the need for separatediodes. The second and third switches S2, S3 may be bidirectionalswitches formed from series-connected IGBTs Q2, Q3, Q4, Q5 withrespective diodes D4, D5, D6, D7. According to further embodiments,instead of the two-core arrangement illustrated in FIG. 1, a busbalancer apparatus 100″ according to further embodiments may includewindings L1, L2, L3, L4 wound on a single common core 412, as shown inFIG. 4.

The control circuit 120 of FIGS. 1, 3 and 4 may be implemented using anyof variety of different analog and/or digital circuit components. Forexample, the control circuit 120 may be implemented using a dataprocessing device, such as a microcontroller, along with peripheralcircuitry configured to drive the first, second, third and fourthswitches S1, S2, S3, S4. In some embodiments, the first, second, thirdand fourth switches S1, S2, S3, S4 may be controlled using analog and/ordiscrete digital circuitry that provides similar functionality.

According to further embodiments, bus balancer apparatus along the linesdiscussed above may be used to balance voltages across other types ofdevices, such as serially-connected batteries or other energy storagedevices. For example, FIG. 5 illustrates the use of the bus balancerapparatus 100″″ similar to the balancer apparatus 100″ of FIG. 4, exceptfor the removal of the neutral connection and addition of a switch S5,which may be used to balance voltages across batteries in a string ofserially-connected batteries B1, B2, B3, B4. The switches S1, S2, S3,S4, S5 may be operated at a common near 50% duty cycle along linesdiscussed above. Such an arrangement may be particularly advantageousin, for example, lithium-ion battery systems, in which maintainingequilibrium among cells in a battery string may be important inpreventing thermal runaway. Further applications of balancer apparatusinclude balancing of capacitors for multi-level converters. For example,FIG. 6 illustrates the use of the balancer apparatus 100″ of FIG. 4 inconjunction with a 5-level inverter 20.

Balancer apparatus according to some embodiments of the inventivesubject matter are also scalable for strings having larger numbers ofenergy storage devices. For example, FIG. 7 illustrates a balancerapparatus 700 configured to balance voltages across six capacitors C1,C2, C3, C4, C5, C6 that are serially connected between first and secondDC buses 105 a, 105 b that feed a 7-level inverter 30. The apparatus 700includes six series-connected windings L1, L2, L3, L4, L5, L6 wound on acommon core 712. A first switch S1 is configured to couple a firstterminal of the first winding L1 to the first DC bus 105 a. A secondswitch S2 is configured to connect a second terminal of the firstwinding L1 and a first terminal of the second winding L2 to a medialnode of the string of capacitors C1, C2, C3, C4, C5, C6 at which thefirst and second capacitors C1, C2 are connected. A third switch S3 isconfigured to couple a second terminal of the second winding L2 to amedial node of the string of capacitors C1, C2, C3, C4, C5, C6 at whichthe second and third capacitors C2, C3 are connected. A second terminalof the third winding L3 and a first terminal of the fourth winding L4are connected to a neutral node N at which the third and fourthcapacitors C3, C4 are connected. A fourth switch S4 is configured toconnect a second terminal of the fourth winding L4 and a first terminalof the fifth winding L5 to a medial node of the string of capacitors C1,C2, C3, C4, C5, C6 at which the fourth and fifth capacitors C4, C5 areconnected. A fifth switch S5 is configured to connect a second terminalof the fifth winding L5 and a first terminal of the sixth winding L6 toa medial node of the string of capacitors C1, C2, C3, C4, C5, C6 atwhich the fifth and sixth capacitors C5, C6 are connected. A sixthswitch S6 is configured to connect a second terminal of the sixthwinding L6 to the second DC bus 105 b. A first diode D1 is connectedbetween the second terminal of the sixth winding L6 and the first DC bus105 a, and a second diode D2 is coupled between the first terminal ofthe first winding L1 and the second DC bus 105 b.

The windings L1, L2, L3, L4, L5, L6 have an approximately 1:1 turnsratio and a control circuit 720 controls the first, second, third,fourth, fifth and sixth switches S1, S2, S3, S4, S5, S6 such that thefirst, second, third, fourth, fifth and sixth switches S1, S2, S2, S3,S4, S5, S6 operate at the substantially the same duty cycle. In someembodiments, the first, second, third, fourth, fifth and sixth switchesS1, S2, S3, S4, S5, S6 may be operated at a duty cycle of around 50%. Itwill be appreciated that this arrangement can be expanded to stringswith even greater numbers of energy storage devices (e.g., capacitors,batteries, supercapacitors) using additional windings and switches.Although the embodiments described above are used to balance voltagesfor strings having an even number of energy storage devices, furtherembodiments may similarly use an odd numbers of winding to balancestrings with a corresponding odd number of serially-connected energystorage devices.

According to additional aspects, multiple balancer apparatus along thelines described above operating in an interleaved fashion may be used toprovide improved performance. Referring to FIG. 8, first and secondbalancer apparatus 100 a″, 100 b″ similar to the balancer apparatus 100″of FIG. 4 are provided. As shown in FIG. 9, the switches S1, S2, S3, S4of the first and second balancer apparatus 100 a″, 100 b″ are operatedat around a 50% duty cycle and in a complementary fashion such that theswitches S1, S2, S3, S4 of the first balancer apparatus 100 a″ are “off′when the switches S1, S2, S3, S4 of the second balancer apparatus 100 b”are “on,” and the switches S1, S2, S3, S4 of the second balancerapparatus 100 b″ are “off” when the switches S1, S2, S3, S4 of the firstbalancer apparatus 100 a″ are “on.” This enables balancing to occur on asubstantially continuous basis.

In the drawings and specification, there have been disclosed exemplaryembodiments of the inventive subject matter. Although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the inventive subject matterbeing defined by the following claims.

That which is claimed:
 1. An apparatus comprising: first, second, thirdand fourth serially connected windings; a first switch configured toconnect a first tap of the first winding to a first terminal of a firstenergy storage device; a second switch configured to connect a secondtap of the first winding and a first tap of the second winding to asecond terminal of the first energy storage device and first terminal ofa second energy storage device, the second tap of the second winding anda first tap of the third winding connected to a second terminal of thesecond energy storage device and a first terminal of a third energystorage device; a third switch configured to connect a second tap of thethird winding and a first tap of the fourth winding to a second terminalof the third energy storage device and a first terminal of a fourthenergy storage device; a fourth switch configured to connect a secondtap of the fourth winding to a second terminal of the fourth energystorage device; and a control circuit configured to operate the first,second, third and fourth switches at a same duty cycle.
 2. The apparatusof claim 1 wherein the first and second windings are magneticallycoupled to one another and wherein the third and fourth windings aremagnetically coupled to one another.
 3. The apparatus of claim 2,wherein the first and second windings are wound on a first core andwherein the third and fourth windings are wound on a second core.
 4. Theapparatus of claim 2, wherein a turns ratio of the first winding to thesecond winding is 1:1 and wherein a turns ratio of the third winding tothe fourth winding is 1:1.
 5. The apparatus of claim 1, wherein thefirst, second, third and fourth windings are magnetically coupled to oneanother.
 6. The apparatus of claim 5, wherein the first, second, thirdand fourth windings are wound on a common core.
 7. The apparatus ofclaim 5, wherein a turns ratio of the first, second, third and fourthwindings to one another is 1:1.
 8. The apparatus of claim 1, wherein theduty cycle is less than 50%.
 9. The apparatus of claim 8, wherein theduty cycle is greater than 40%.
 10. The apparatus of claim 1, furthercomprising: a first diode connected between the first terminal of thefirst energy storage device and the second terminal of the fourthwinding; and a second diode connected between second terminal of thefourth energy storage device and first terminal of the first winding.11. The apparatus of claim 1, wherein the first, second, third andfourth switches are bidirectional.
 12. The apparatus of claim 11,wherein the first and third switches each comprise an insulated gatebipolar transistor (IGBT) and a diode coupled in parallel with the IGBT.13. The apparatus of claim 1, wherein the second and fourth switcheseach comprise two IGBTs coupled in series and respective diodes coupledin parallel with the IGBTs.
 14. The apparatus of claim 1, wherein thefirst, second, third and fourth energy storage devices comprisecapacitors or batteries.
 15. The apparatus of claim 1, furthercomprising a multilevel inverter circuit coupled to the terminals of thefirst, second, third and fourth energy storage devices.
 16. An apparatuscomprising: a string of serially-connected energy storage devices; astring of serially-connected windings on at least one core and having afirst medial node coupled to a first medial node of the string ofserially-connected energy storage devices; and first and second switchesconfigured to connect first and second end nodes of the string ofserially-connected storage devices to respective first and second endnodes of the string of serially-connected energy storage devices; and acontrol circuit configured to operate the first and second switches atthe same duty cycle.
 17. The apparatus of claim 16, wherein the stringof serially-connected energy storage devices comprises at least fourserially-connected energy storage devices; wherein the string ofserially-connected windings comprises at least four serially-connectedwindings; and third and fourth switches, respective ones of which areconfigured to connect respective second and third medial nodes of thestring of serially-connected windings to respective second and thirdmedial nodes of the string of serially-connected energy storage devices.18. The apparatus of claim 17, wherein the at least fourserially-connected windings are wound on a single core.
 19. Theapparatus of claim 16, wherein the string of serially-connected energystorage devices comprises capacitors or batteries.
 20. The apparatus ofclaim 16, further comprising a multi-level inverter coupled to thestring of serially-connected energy storage devices.